Re:Stepper Motor vs Servo Motor

I was hoping someone could clarify a few points for me.

What is the practical difference between AC and DC, brush and brushless servos?

Is there a difference between an encoder and a tach? Or is RPM just a calculated by the controller from the encoders feedback?

I've seen servos that don't look like they have encoders on them. Are servos often sold with the feedback hardware?

In one of the classrooms at school sits an old (plaque says 1967) NC Bridgeport. The brain for this machine was "accidentally thrown away at least 10 years ago. The Chairman of the dept says I can have it if I do all the paper work. It has no manual control, but I thought an upgrade might render me a good machine. It has "slo-syn" steppers ( I think they are steppers as they don't seem to have any type of encoder/feedback provision) and acme screws, however for the type of work I want to do, I think (from what I�ve read here mostly) that ballscrews and servos are what I would want to use.

The steppers that are on the machine are 400oz/in so I figured that I should find servos that are at least that powerful does this sound right? Likewise can the gecko 320s handle motors this big? If not does it require a driver with a higher current rating?

Thanks

Peter-

I have a few other questions, but I'll save them for another post, as I get closer to saving the money I need to start buying components.



---------------------------------
Do You Yahoo!?
Sign-up for Video Highlights of 2002 FIFA World Cup

[Non-text portions of this message have been removed]